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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Util
  9. {
  10.     public static Class mostDerived(Collection<?> objects) {
  11.         Optional<List<Class<?>>> mostDerived =
  12.             objects.stream()
  13.                    .map(Util::getHierarchy)
  14.                    .reduce((l1, l2) -> {
  15.                        l1.retainAll(l2);
  16.                        return l1;
  17.                    });
  18.         return mostDerived.map(l -> l.get(0)).orElse(null);
  19.     }
  20.  
  21.     private static List<Class<?>> getHierarchy(Object l) {
  22.         List<Class<?>> result = new ArrayList<>();
  23.         for (Class<?> clz = l.getClass(); clz != null; clz = clz.getSuperclass()) {
  24.             result.add(clz);
  25.         }
  26.         return result;
  27.     }
  28.  
  29.     public static void main(String[] args) {
  30.         assertEquals(A.class, Util.mostDerived(Arrays.asList(new B(), new B(), new C(), new A(), new B())));
  31.         assertEquals(B.class, Util.mostDerived(Arrays.asList(new C(), new B(), new C(), new C(), new B())));
  32.         assertEquals(A.class, Util.mostDerived(Arrays.asList(new B(), new D(), new B())));
  33.     }
  34.  
  35.     private static void assertEquals(Class<?> aClass, Class mostDerived) {
  36.         if (!aClass.equals(mostDerived)) {
  37.             throw new RuntimeException();
  38.         }
  39.     }
  40. }
  41.  
  42.  
  43. class A {};
  44.  
  45. class B extends A {};
  46.  
  47. class C extends B {};
  48.  
  49. class D extends A {};
  50.  
Success #stdin #stdout 0.14s 2184192KB
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https://ideone.com/GokBsw
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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